Storing struct as a field

[fdorothy]

I'm pretty new to Rust and JNI, so sorry if this is a bad question.

Is there a way to store a raw pointer to a struct as a field?

For example, I have a complex structure named Runtime. This has properties that won't serialize to Java, but that's fine, I just want a reference to it and use its functions on the Rust side. I was thinking I could add runtime as a field using JObject:

    #[derive(Signature, TryIntoJavaValue, IntoJavaValue, TryFromJavaValue)]
    #[package()]
    pub struct JniRunner<'env: 'borrow, 'borrow> {
        #[instance]
        raw: AutoLocal<'env, 'borrow>,
        #[field]
        runtime: Field<'env, 'borrow, JObject<'env>>,
    }

However, I'm not clear on how to convert my Runtime struct into a JObject using this package's version of JNI. I was thinking I could do something like below, but JNI 0.19.0 doesn't have the from_raw method on JObject:

let raw_ptr = Box::into_raw(Box::new(Runtime {}));
self.runtime.set(unsafe { JObject::from_raw(raw_ptr as jobject) });

Is there a better way to store a raw pointer to a complex struct in robusta?

[giovanniberti]

Hi!
I don't think there is a much better way right now (regarding your question about jni 0.19: you could cast the raw pointer to *mut Runtime and then to *mut _jobject and use that with JObject::from).

If Runtime implemented IntoJavaValue or similar you could use its conversion methods, but if it doesn't then I think yours is the only way.

[fdorothy]

Hello and thanks!

I've gotten a bit further along thanks to your help. I am now running into an issue where the JObject doesn't appear to be getting set by self.runtime.set(jobj) (which is a field). My code:

#[field]
runtime: Field<'env, 'borrow, JObject<'env>>,

...

let raw_ptr = Box::into_raw(Box::new(runtime));
let jobj = JObject::from(raw_ptr as jobject);
println!("{:#?}", jobj);
self.runtime.set(jobj)?;
println!("{:#?}", self.runtime.get()?);

This outputs the following:

JObject {
    internal: 0x0000600002668700,
    lifetime: PhantomData<&()>,
}
JObject {
    internal: 0x0000000000000000,
    lifetime: PhantomData<&()>,
}